91 lines
2.2 KiB
Java
91 lines
2.2 KiB
Java
/*
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* Name: Mike Cifelli
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* Course: CIS 443 - Programming Languages
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* Assignment: Lisp Interpreter 2
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*/
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package eval;
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import parser.*;
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import java.util.HashMap;
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/**
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* A <code>SymbolTable</code> maps symbol names to values.
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*/
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public class SymbolTable {
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private HashMap<String, SExpression> table;
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private SymbolTable parent;
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/**
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* Create a new symbol table with no parent.
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*/
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public SymbolTable() {
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this(null);
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}
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/**
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* Create a new symbol table with the specified parent.
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*
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* @param parent
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* the parent of this symbol table
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*/
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public SymbolTable(SymbolTable parent) {
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this.table = new HashMap<String, SExpression>();
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this.parent = parent;
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}
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/**
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* Determine if the specified symbol name is in this symbol table.
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*
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* @param symbolName
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* the name of the symbol to look up
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* @return
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* <code>true</code> if the symbol is in this symbol table;
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* <code>false</code> otherwise
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*/
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public boolean contains(String symbolName) {
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return table.containsKey(symbolName);
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}
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/**
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* Returns the value to which the specified symbol name is mapped in this
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* symbol table.
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*
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* @param symbolName
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* the name of the symbol whose associated value is to be returned
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* @return
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* the value to which this symbol table maps <code>symbolName</code>, or
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* null if no mapping exists
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*/
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public SExpression get(String symbolName) {
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return table.get(symbolName);
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}
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/**
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* Associates the specified symbol name with the specified value in this
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* symbol table. If the symbol table previously contained a mapping for
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* this symbol name, the old value has been replaced.
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*
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* @param symbolName
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* the name of the symbol with which the specified value is to be
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* associated
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* @param value
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* the value to be associated with the specified symbol name
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*/
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public void put(String symbolName, SExpression value) {
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table.put(symbolName, value);
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}
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/**
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* Returns the parent of this symbol table.
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*
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* @return
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* the parent of this symbol table
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*/
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public SymbolTable getParent() {
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return parent;
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}
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}
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